This invention relates to the utilization of waste heat, and particularly to a heat recovery device for interposing in a flue duct carrying off hot gases and products of combustion from a furnace or the like.
I am aware of examples of heat recovery devices in the prior art, for example water heater accessories as shown in Goldhagen No. 1,865,852 and Marquez No. 3,793,992. In the instance of the former example, a coil for circulation of water to be heated is positioned within a flue section adapted to be inserted in a furnace flue duct. The interior location of the water coil is hazardous since a leaking coil can extinguish the furnace flame and allow an accumulation of unburned gas or oil. In addition, products of combustion depositing on the coil create a layer of insulation causing a steadily decreasing level of heat transfer efficiency. In the instance of the latter example, that is, Marquez 3,793,992, the water coil is external to the flue duct but is nested in an insulating material. Application of the coil is to an existing flue duct, and not to a flue section which is an integral part of the device. Heat transfer efficiency accordingly varies with the aptitude of the installer and with multiple tolerances as represented by the flue duct diameter, coil tubing diameter and the depth of coil accommodating grooves in the insulator. Just how the reference device is applied is unclear, but it has no existence as a device capable of being handled, stored and installed as a unit in to become a part of a flue duct.